Sorption of fluoride by quartz sand: batch tests.

EDUARDO USUNOFF; PABLO WEINZETTEL; SEBASTIÁN DIETRICH

Geoacta

Asociación Argentina de Geofísicos y Geodestas

Lugar: Buenos Aires; Año: 2009 vol. 34 p. 9 - 17

0326-7237

Despite the many  efforts of scientists, in particular those fiom the  field of soil  science,  the  fate and distribution of fluorine  (F) species  in soils and aquifers  remain relatively unraveled. As for groundwater systems, such a shortcoming makes difficult the  findiig and development of  safe water supplies.  Likewise, the use of transport models does not render acceptable results because of the many uncertainties  related to the behavior of F in aqueous media. This paper presents  the results of  four batch  test in which solutions  of different pH and [F-]  (concentration of fluoride) were in contact during 48 hours with clean quartz sand grains. The  resulting data were fitted by  linear versions of the Freundlich, the Langmuir, and the Langmuir-Freundlich models. The [F-] was varied between 0,s and 10 mg L-´, except  in one batch where a large  initial concentration of F was used (45 mg L-´),  and  the range of pH used was 2,95  to 5,02. From a sieve analysis, the quartz grains  had a medium size  (d,,,) of 0,25 mm, and a uniformity  coefficient  (ddd,)  of 1,65. According to the fits and some dedicated goodness of fit  indices, the Langrnuir-Freundlich approach gave the best results for the batch test  at the  lowest pH, whereas the three remaining tests data were fitted by  the Freundlich equation. It has to be mentioned that the pH of the equilibrium solutions were higher  than the pH of the initial solutions, which was interpreted as an exchange process of OH-  by F-  on the quartz sand  surface. However,  such an exchange does not  stand out as the exclusive mechanism promoting the F- disappearance fiom solution. It is deemed that the obtained results can be used  as initial estimates of parameters  in models used for calibrating the transport of F- in aquifers.